[Exim] Mail Loop with Firewall and Relay Domain

I'm getting mail loops because (I think) that Exim doesn't realize who it
is. Let me explain...

renaghan.com has the following MX records
renaghan.com.           1H IN MX        0 mail.montanab.com.
renaghan.com.           1H IN MX        5 renaghan.net.

Host mail.montanab.com was down for 10+ hours last night, so most mail
destined for renaghan.com was being relayed to renaghan.net

renaghan.net is my home firewall box at 208.58.67.63, known internally as
dublin.local (internal IP 10.10.1.1).

renaghan.net has an IPTABLES port forward setup so that any connection to
208.58.67.63 on port 25 is forwarded to an internal machine 10.10.1.50 on
port 25. The internal machine is known as "cork.local".

I started getting mail loops for mail destined for renaghan.com that was
being relayed through renaghan.net.

I think what is happening is that cork.local gets mail for renaghan.com
which it knows it is a relay domain for. The cork.local goes to forward
the message along, renaghan.com is still down, so it trys the next highest
MX which is renaghan.net. It opens a connection to renaghan.net, which
ends up being port forwarded back to cork.local, so cork ends up
delivering the message to itself.

Yes, I do have "primary_hostname = renaghan.net" set in the exim config on
cork.local.

Any ideas what is happening?

Is my guess about what is causing the mail loops possible?

Below is a copy of the rcvd headers for a message that got caught in this
loop.

Thanks,
Padraic

Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pz-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001px-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pv-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pt-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pr-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pp-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pn-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7k-0001pl-00
        for padraic@???; Tue, 18 Sep 2001 19:17:52 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pj-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001ph-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pf-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pd-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pb-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pZ-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pX-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pV-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7j-0001pT-00
        for padraic@???; Tue, 18 Sep 2001 19:17:51 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pR-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pP-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pN-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pL-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pJ-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pH-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pF-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pD-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001pB-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7i-0001p9-00
        for padraic@???; Tue, 18 Sep 2001 19:17:50 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7h-0001p7-00
        for padraic@???; Tue, 18 Sep 2001 19:17:49 -0400
Received: from dublin.local ([10.10.1.1] helo=renaghan.net)
        by renaghan.net with ESMTP (Exim)
        id 15jU7h-0001p5-00
        for padraic@???; Tue, 18 Sep 2001 19:17:49 -0400
Received: from [24.254.60.16] (helo=femail26.sdc1.sfba.home.com)
        by renaghan.net with ESMTP (Exim)
        id 15jU7h-0001p3-00
        for padraic@???; Tue, 18 Sep 2001 19:17:49 -0400
Received: from c1388035a ([65.4.0.247]) by femail26.sdc1.sfba.home.com
          (InterMail vM.4.01.03.20 201-229-121-120-20010223) with SMTP
          id
<20010918231403.BLZD12095.femail26.sdc1.sfba.home.com@c1388035a>
          for <padraic@???>; Tue, 18 Sep 2001 16:14:03 -0700